Down draft stove control



July 2, 1957 e. w. HARDING DOWN DRAFT STOVE CONTROL 2 Sheets-Sheet 1 Filed Jan. 12, 1954 INYENTOR d. lfi vzdly ATTORNEYS July 2, 1957 a. w. HARDING DOWN DRAFT STOVE CONTROL 2 Sheets-Sheet 2 Filed Jan. 12, 1954 I 1 I I 1 ATTORNEYS 1 2,797,874 Patented July 2, 1957 DOWN DRAFT STOVE CONTRGL George W. Harding, Lynchburg, Va., assignor to Automatic Draft and Stove Co., Inc, Lynchburg, Va, a corporation of Virginia Application January 12, 1954, Seriai No. 403,497

(Ilaims. (Cl. 236-86) This invention relates to down draft heating stoves, and particularly to that type of stove in which combustion is thermostatically controlled primarily responsive to stove temperature rather than room temperature. It is a fact of common knowledge that wood burning heating stoves are for the most part used in rural homes that are uninsulated and drafty, so that on account of the labor of providing the prodigious quantity of wood for heating the entire room, it is more practical to maintain a more restricted comfortable zone of substantially uniform temperature in the vicinity of the stove, which is done by controlling the combustion responsive to the temperature of the stove.

It has been the experience with those stoves in which combustion is controlled responsive to stove temperature, that under conditions of diminishing combustion, the heat from a low fire communicating through the metal parts of the stove to the thermostat is still sufiicient to keep the damper closed beyond the critical point at which the fire may be revived so that notwithstanding belated opening of the damper, the fire goes out.

One of the objects of the present invention is to provide a stove of the general type described, in which the damper controlling thermostat is made responsive to a temperature factor, the major component of which is derived directly from the stove, and the minor component being from the cooler room atmosphere. Thus, under conditions of diminishing combustion, the temperature at which the thermostat opens the damper is reached sooner than if the thermostat were affected by stove heat alone, and combustion is stimulated before becoming reduced to the point at which thereis no recovery.

A more specific object of the invention is to provide a casing for the thermostatic damper control designed to protect the thermostat from temperature variations extraneous to the aforementioned control components of the temperature factor.

Other objects of the invention will appear as the fol lowing description of a preferred and practical embodiment of the invention proceeds.

In the drawings which accompany and form a part of the following specification, and throughout the several figures of which the same characters of reference have been employed to denote identical parts:

Figure 1 is a perspective view of a down draft wood burning heating stove embodying the features of the invention;

Figure 2 is a fragmentary vertical sectional View taken along the line 2-2 of Figure 1;

Figure 3 is a vertical cross-section taken along the line 33 of Figure 2;

Figure 4 is a horizontal cross-section taken along the line 4-4 of Figure 2;

Figure 5 is a perspective view of the damper supporting frame.

Referring now in detail to the several figures, the numeral 1 represents as a whole a stove of the type described, having the cylindrical drum or combustion chamber 2, a laterally swingable lid 3, for filling, and the chimney pipe 4. In common with most down draft wood burning stoves it is characterized by the absence of any air inlet through its lower wall open directly to atmosphere. A down draft flue 5 is formed inside the drum 2 between the curved front wall of the drum and a flat plate 6 arranged in a vertical plane, chordally of the drum, having lateral flanged margins '7 secured against the inner wall of the drum, and an outwardly turned flange 8 at the top having a curved peripheral edge which meets the wall of the combustion chamber and forms a top closure for the fine. The lower edge 9 of the plate 6 terminates above the bottom of the stove, defining therewith an inlet 10 to the lower part of the combustion chamber.

The drum 2 has an opening 11 through its front wall at the top, which is overlain on the outside of the drum by the casing 12 which houses the automatic down draft control means. The down draft flue extends above the bottom of the opening 11 and through it communicates with the casing 12.

Said casing comprises a rectangular tubular conduit 13 (see Figure 2) having a closed bottom and a perforated top cover 14, the perforations 15 of which constitute the air inlet of the down draft flue, said conduit being an external continuation of the down draft flue. Intermediately, the conduit 13 is divided by a damper 16 which controls the passage of air through said flue. In front of the conduit 13 and contiguous thereto is a vertical duct 17 of rectangular cross-section having an opening 18 at its bottom, and being overlain by the top cover 14 having perforations 19 communicating with said duct. The damper 16 has a stem 20 that extends into the duct 17. A bimetallic spring 21 which constitutes the thermostat is fixed at one end to the stem and anchored at its other end to a fulcrum pin 22 on an arm 23, which extends radially from the shank 24. An adjusting knob 25 is on the outer end of the shank 24 and movable with reference to an indicating dial 26 on the outer face of the casing. The knob and arm 23 are rotatable under heavy friction to shift the fulcrum pin 22 and twist or untwist the thermostat to give the damper an advanced or retarded initial setting with respect to its closing position, which setting is the datum from which the thermostatic control begins to operate.

The metal parts of the casing 12 being in thermal continuity with the drum 2, will be heated by conductivity from the walls of said drum. This incidentally somewhat preheats the air entering the down draft flue 5 through the perforation 15', the air being further preheated before it enters the combustion chamber by its passage through the internal portion of the down draft flue. The most important function of the heat transmitted to the casing is, however, its efiect upon the thermostat 21, causing it to move the damper in a closing direction responsive to increase in heat and in opening direction when the heat decreases.

The duct 17 is a passage for room air which moves upward through said duct by convection, entrained by the rising warm air in the vicinity of the stove. The thermostat is directly bathed by this upwardly drawn column of air which is relatively cool, since it comes from near the floor, and is decidedly cooler than the metal walls of the casing 12. The heat conducted to the thermostat through the metal casing and damper, and the cold air conveyed to the thermostat by the flow of room air through the duct 17 are the two components of the temperature factor to which the thermostat responds.

Since this mean temperature is lower than the temperature conducted by the metal parts, the thermostat will open sooner under conditions of a declining fire than it would if responsive solely to the temperature of the stove.

The casing which houses the thermostatic damper control means is strictly designed to promote efficiency of operation of the thermostatic damper, and'ease in manufacture'and assembly. Said casing specifically comprises a three sided rectangular shell 26, having the same height and width as corresponding dimensions of the opening 11, being placed in front of said opening, with its fourth or open side congruent therewith. Said shell has lateral flanges 27 engaging the drum 2 at the sides of the opening 11, and being secured to the drum by suitable means such as the stove bolts 28. The shell 26 is divided into upper and lower compartments by a box-like'frame 29 fitted transversely thereacross and secured thereto. The-upper compartment is closed by a back plate 30 outwardly flanged at its top and sides and secured laterally to the sides of said shell. The top flange 31 is curved along its outer edge to fit against the drum 2 just above the top of the opening 11.

The frame 29, which is shown in perspective in Figure 5, has a vertical perimetric flange 28', the sides of which engage corresponding sides of the shell26, while the fourth side engages the lower part of the back plate and is secured thereto. Said frame has an outwardly extending horizontal flange 32 all around, forming a seat for the damper 16 which controls the opening bounded by said horizontal flange. rectangular notches 33 at the middle of two opposite sides. The stem 20 of the damper is journaled in the frame 29 below said notches, with its axis in a vertical plane intersecting said notches. That part of the flange 32 on one side of said axis lies in a plane slightly higher than that part which lies on the other side of said axis, so that the damper which is planiform engages the under. side of one-half of the flange 32 and the upper side of the other half. The damper extends from one level to the other through said notches, so that the back edges of said notches act as limit stops to prevent endwise movement of the damper and thereby to retain the ends of the stem 20 within its bearings. The front of the shell 26 has a vertical slot 4 extending from its upper edge to a point below the damper stem. This slot was useful in installing the frame 29, together with the damper, in the shell.

A three sided rectangular sheath 35 of the same height and substantially the same width as the shell 26 rests over the latter, having lateral flanges 36 which congruent- The latter is provided with ly overlie the corresponding flanges 27 of the shell and are secured by the bolts 28. The sheath 35 projects forwardly beyond the shell 26, defining with the front wall thereof the duct 1'7 which contains the thermostat.

Finally, the sheath 35 is surrounded by a housing 37, folded to form a front panel 38 congruently overlying the front of the sheath 35, and a pair of similar Wings 39 extending divergently from the front panel, and having flanges 40 at their ends secured by bolts 41 to the drum 2 at points circumferentially displaced with respect to the points of securement of the shell and sheath to said drum. The housing 37 is of the same height as the shell and sheath, and has no bottom. It is closed at the top by the cover 14. That part of said cover which overlies the space between the sheath 35 and wings 39 is imperforate, so that said spaces are dead air chambers open only at the bottom, which retain air warmed by the surrounding metal walls, and which protect the side walls of the shell from drafts, thus maintaining a substantially steeper rate of heat exchange between the heated walls of the conduit 13 (the external part of the down draft flue) and the thermostat. The double thick character of the side walls of said conduit provides additional means for the conduction of maximum heat from the drum 2 to the thermostat.

It will be understood by those skilled in the art that I have devised a down draft wood burning heating stove with thermostatic damper control predominately responsive to stove temperature, but in which the heat factor to which the thermostat responds is a composite of combustion temperature which is variable according to combustion conditions, and room temperature which imposes a cooling influence upon the heat factor throughout the control range, the effect of which is negligible throughout the higher range of stove heat but becomes controlling under lower conditions of stove heat so as to open the damper before the combustion declines to the critical point below which the fire cannot be revived.

It will also be apparent that I have invented a stove of the type described, in which the damper may be set to control the stove through any range of combustion activity that may be desired, and that with such selective setting as a datum, the thermostatic damper control takes over the automatic control. It will also be understood that by the novel construction of the casing which forms the external part of the down draft flue, optimum efiiciency of operation and uniformity of control are achieved.

' What I claim is:'

1. Down draft heating stove comprising a drum forming a combustion chamber, including a side wall having an opening into said drum near the top, means forming a down draft flue within said combustion chamber, a casing secured to the outside of said drum comprising upright walls arranged in nested relation, said walls including a conduit forming wall having its sides relatively spaced and secured to said drum, a conduit being thereby formed between said wall and drum, a duct forming wall overlying said conduit forming wall having its sides contiguous to the sides of said conduit forming wall and being of greater depth from front to back whereby a duct is formed between the intermediate parts of said walls, the sides of said duct forming wall being secured to said drum, and a housing wall overlying said duct forming wall having its front portions engaging the intermediate part of said duct forming wall and its sides flared with respect to the sides of said duct forming wall, said sides being secured to said drum at points spaced from the sides of said duct forming wall whereby to form chambers laterally of said conduit and duct, a damper dividing said conduit into upper and lower compartments, said lower compartment being in open registry with said drum opening, and said upper compartment being open to atmosphere forming an air inlet for said down draft flue, said duct forming a passage for the convectional upward flow of room air, said damper having an operating stern extending into said duct, a thermostat in said duct having one end secured to said stem, means forming a shiftable fulcrum for said thermostat and means on the outside of said casing for selectively shifting said fulcrum, said casing have a top cover overlying said chambers whereby they constitute dead air spaces.

2. Down draft heating stove as claimed in claim 1, said top cover being coextensive with the space embraced by said housing and being perforated above said conduit and above said duct.

3. Down draft heating stove comprising a drum forming a combustion chamber having an opening in its side .wall near the top, means forming a down draft flue within said combustion chamber, a casing secured to the outside of said drum comprising three wall forming members of uniform height arranged in nested relation, said members including a three sided rectangular conduit forming a continuation of said down draft flue having outwardly turned flanges along itslateral edges, a three sided sheath of substantially the same width as said conduit but being of greater depth, and having outturned lateral edge flanges, said sheath being in telescoped relation over said conduit with its lateral flanges congruently engaging the flanges of said conduit and being commonly secured to said drum, and a housing having a front panel arranged in congruent engagement with the front of said sheath and having wings extending divergently from said front panel with drum at points more widely spread circumferentially than the points of securement of said conduit and sheath, a damper dividing said conduit into upper and lower compartments, said lower compartment being in open registry with said drum opening and said upper compartment being open to atmosphere forming an air inlet for said down draft flue, the space between the front of said conduit and of said sheath forming a duct for the convectional upward flow of room air, said damper having an operating stem extending into said duct, a thermostat in said duct having one end secured to said stern, means forming a shiftable fulcrum for said thermostat and means on the outside of said casing for selectively shifting said fulcrum, and a top cover for said casing coextensive with the space embraced by said housing, perforated above said conduit and duct and imperforate above the spaces between said sheath and wings whereby dead air spaces are formed between said sheath, wings and drum.

4. Down draft heating stove as claimed in claim 3, including a back plate for the upper compartment of said conduit forming the fourth side of said compartment, having outwardly turned lateral flanges secured to the sides of said conduit, and an outwardly turned top flange the free edge of which fits the curvature of said drum, and

a rectangular frame fitting said conduit in which said damper is journaled, said frame being secured to said back plate.

5. Down draft heating stove as claimed in claim 3, including a back plate for the upper compartment of said conduit forming the fourth side of said compartment, having outwardly turned lateral flanges secured to the sides of said conduit and an outwardly turned top flange the free edge of which fits the curvature of said drum, a rectangular frame in which said damper is journaled, said frame fitting said conduit and being secured to said back plate, said frame having an interior peripheral flange, the half of which on one side of the axis of rotation of said damper is at a slightly higher level than the other half whereby the damper closes against the under side of one-half of said flange and against the upper side of the other half, said flanges being formed with rectangular notches intersected by the vertical plane embracing the axis of rotation of said damper, the back edges of said notches preventing endwise slippage of said damper.

References Cited in the file of this patent UNITED STATES PATENTS 610,260 Culter Sept. 6, 1898 974,290 Merritt Nov. 1, 1910 1,133,090 Broomell Mar. 23, 1915 1,919,330 Hornung July 25, 1933 2,607,335 Harding Aug. 19, 1952 

